1. Field of the Invention
The present invention relates to a gate insulating film of a semiconductor device, for example, MOSFET. In particular, the present invention relates to a method of manufacturing an insulating film containing hafnium (Hf).
2. Description of the Related Art
Currently, a silicon oxide film and a silicon nitride film are used as a gate insulating film of a MOSFET. The gate insulating film must be formed having a sub-nm size because scale reduction of the MOSFET advances and its performance is improved. For this reason, a gate leakage current remarkably increases by the direct tunnel effect. Thus, it is difficult to use the silicon oxide employed in the conventional case in future.
In recent years, practically using a high-dielectric-constant material called a high-k material as a gate insulating film has been researched. For example, HfO2 is given as the high-dielectric-constant material. The foregoing HfO2 is very hopeful because it has relatively high dielectric constant and wide band gap.
However, when HfO2 is used as a gate insulating film, the following problem arises. Specifically, silicidation or crystallization of HfO2 is produced at the interface between a HfO2 gate insulating film and a polysilicon layer as a gate electrode by high-temperature heat treatment in the manufacturing process. In other words, if the HfO2 used as the gate insulating film is crystallized, gate leakage current is generated through grain boundaries. For this reason, wasteful power consumption is produced. Moreover, when a part of the gate insulating film is formed as silicide, a current path will arise in the gate insulating film by the silicide.
Thus, there has been made the research of preventing silicidation and crystallization of HfO2 (see T. Takahashi, S. Toyoda, J. Okabayashi, H. Kumigashira, M. Oshima, Y. Sugita, G. L. Liu, Z. Liu, and K. Usuda, “Chemical reaction at the interface between polycrystalline Si electrodes and HfO2/Si gate dielectrics by annealing in ultrahigh vacuum”, 2005 American Institute of Physics, Applied Physics Letters 87, 012903 (2005), published online 29 Jun. 2005). According to the research, for example, a HfO2 film is formed on a silicon layer, a sample formed with a polysilicon layer on the HfO2 film is heated in ultrahigh vacuum. In this case, the following reaction occurs, and then, 2SiO is released as gas. Further, silicidation of hafnium is produced, and crystallization of the HfO2 film was confirmed. For this reason, it is difficult to prevent silicidation and crystallization.4Si+HfO2→2SiO+HfSi2 
When the sample is heated in an oxygen atmosphere, and thereby, a generation of SiO and silicidation were prevented. However, excessive oxygen is supplied to the HfO2 film; for this reason, it was difficult to prevent crystallization of the HfO2 film.
In addition, when the sample is heated in a nitrogen atmosphere, and thereby, SiO is produced, and silicidation of the HfO2 film occurs. Therefore, it was difficult to prevent crystallization of the HfO2 film.
As described above, it was conventionally difficult to prevent both of silicidation and crystallization of an insulating film containing hafnium. Therefore, it is desired to a method of manufacturing a semiconductor device, which can prevent both of silicidation and crystallization of an insulating film containing hafnium.
For example, the following document discloses the research of the mechanism of silicidation of the HfO2 film by forming a sample excluding a polysilicon layer from the sample, and heating it in ultrahigh vacuum.
Document: S. Toyoda, J. Okabayashi, H. Takahashi, H. Kumigashira, M. Oshima, M. Niwa. K. Usuda and G. L. Liu, “Annealing-temperature dependence: Mechanism of Hf silicidation in HfO2 gate insulators on si by core-level photoemission spectroscopy”, 2006 American Institute of Physics, Journal Of Applied Physics 99, 014901 (2006), Published online 3 Jan. 2006.
In addition, the following document discloses the research of the mechanism of crystallization of the HfO2 film.
Document: S. Toyoda, J. Okabayashi, H. Takahashi, H. Kumigashira, M. Oshima, K. Yamashita, M. Niwa. K. Usuda and G. L. Liu, “Crystallization in HfO2 gate insulators with in situ annealing studied by valance-band photoemission and x-ray absorption spectroscopy”, 2005 American Institute of Physics, Journal Of Applied Physics 97, 014507 (2005), Published online 5 May 2005.